The invention relates to a mixture which comprises a transparent polyamide, and also comprises a semicrystalline polyamide that in the pure state is opaque. As a blend, this type of polyamide mixture is transparent; and corresponding moulding compositions have better mechanical properties than the individual components.
Transparent polyamides made of bis(4-aminocyclohexyl)methane (PACM) with from 30 to 70% content of trans,trans-stereoisomer, and also dodecanedoic acid, are known from DE 15 95 150 A1. EP 0 619 336 A2 describes corresponding transparent polyamides made of from 35 to 60 mol % of trans,trans-bis(4-amino-cyclohexyl)methane and from 65 to 40 mol % of other diamines, and also linear aliphatic dicarboxylic acids. According to the description of EP 0 619 336 A2, the transparent polyamides of that type are crystalline; they therefore have good resistance to solvents, and also to stress cracking.
EP 0 725 101 A1 describes transparent, amorphous polyamides which are composed either of alkyl-substituted cycloaliphatic diamines having from 14 to 22 C atoms and of unbranched aliphatic dicarboxylic acids having from 8 to 14 C atoms or of unbranched aliphatic diamines having from 8 to 14 C atoms and of cycloaliphatic dicarboxylic acids. It is mentioned that these polyamides can also be used to produce blends or alloys with aliphatic homopolyamides, but no advantages of any type are alleged for these. No specific relevant examples are disclosed. The amorphous polyamides of described in EP 0 725 101 cannot be based on PACM.
Likewise, EP 0 837 087 A1 does not disclose the use of PACM for the production of the transparent polyamides. It is possible to produce alloys or blends with polyamides such as PA11 or PA12, these likewise being allegedly transparent. Otherwise nothing is said about the properties of alloys or blends with PACM. It remains unclear whether alloys or blends of that type are at all advantageous.
EP 1 595 907 A1 describes transparent amorphous polyamides based on diamines and tetradecanedoic acid, and also mixtures thereof with semicrystalline polyamides. PACM can be used as diamine, and specific mention is made here of PACM20, which comprises 20% of trans,trans-isomer. However, there is no explicit disclosure of the mixture of a PACM-based transparent amorphous polyamide with a semicrystalline polyamide.
The polyamides based on PACM have valuable performance characteristics, and with suitable composition are transparent, but microcrystalline and therefore resistant to solvents and to stress cracking; they have a high level of mechanical properties, for example impact resistance. However, there remains a need for improved puncture resistance. This is important in the application sector of spectacle frames and spectacle lenses, in particular in “sports” applications and “defence” applications. In these applications the material is characterized through a ball-impact test where a ball of defined weight is propelled with a defined velocity onto a spectacle frame or a spectacle lens. Another disadvantage of these polyamides is high melt viscosity under processing conditions, making it difficult to produce filigree components. Although the melt viscosity can be lowered by using the corresponding polyamide with lower molecular weight, this considerably impairs mechanical properties, in particular impact resistance and puncture resistance. The lower molecular weight also leads to lower tensile strain at break, high notch sensitivity and lower ageing resistance on exposure of the mouldings to heat or moisture.
The object of the invention consists in improving the processability of the said polyamides while avoiding any significant impairment of transparency, of resistance to solvents and to stress cracking, and also of mechanical properties. Another aspect of the object consists in improving the puncture resistance, breaking strength, notch sensitivity and ageing performance of corresponding mouldings, while avoiding impairment of transparency, resistance to solvents and to stress cracking.